Ranges obtained by radar altimetry from a satellite to a sloping surface on the earth are not measurements of the surface elevation at the subsatellite point. Instead, the reflecting point is displaced upslope from nadir causing a "slope-induced error" between the true range to the subsatellite point and the indicated range. Ice sheet surface slopes are frequently large enough to cause errors of 10m to 100s of meters. In addition, surface undulations about a mean slope cause pronounced variations in theses errors. This correction is approximated by assuming the ice sheet surface within the beam-limited footprint is planar using the equation:
The calculation of the slope, alpha, is extremely important. The slope correction on the version 4 level 2 data has been calculated from a preliminary 10 km altimetry grid. A full explanation of the problem and the derivation of this equation can be found in (Brenner et al 1983). The error in this correction can be very large. A study is ongoing to try to determine more accurate means of calculating it.
 |
BACK TO PREVIOUS PAGE | | | TOP OF PAGE |
|
Site navigation: Home | Missions | Status | Data Products | Data Processing | Data Distribution | Publications | Links | Site Search | Contact us |
 |
+ Privacy Policy and Important Notices |
 |
Curator: Jairo Santana NASA Official: Dr. H. Jay Zwally Last Updated: 12/11/2006 |